Chlorine demand

[bmj0928]

I have what's called a "Family Fun" pool, meaning it has a plaster bottom (enamel paint) with fiberglass walls. It holds 11,000 gallons.
It's crystal clear, no odor, and no signs of trouble. The issue I am having is that it is eating a gallon of chlorine a day. I was using an auto chlorinator with pucks, but have stopped since joining this site.
I dump the bleach in at night, and get a quick rise to 6 FC and 1 CC, but by morning I am down to 0.5 FC, and 2 CC.

My water is between 88 - 90 degrees, because it's been so warm here in Pittsburgh.

Is it normal to use this much chlorine, or is my CYA too high? Before I partial drain and refill, I just want to check here. Also, I know my TA is a little high, and should acid and aerate.

Test Results:
FC = 0.5
CC= 2 (but fluctuates)
CYA= 90 (high by some standards, within range for those who say >100 is ok)
Ph=7.5
TA=110
CH=400
CSI=0.13

 

[Donldson]

within range for those who say >100 is ok

You won't find any of "those" here. You won't be agreeing with them either in a moment.

You have an issue that requires performing the SLAM Process. This will oxidize whatever is causing the CC issue as well as the organics that are almost certain to be contributing to the chlorine demand (CC and organics are two different sides of the same FC loss coin). As you'll find in the article, you need to follow the FC/CYA Levels to properly SLAM your pool. That means for a CYA of 90 raising your FC up to 35 and keeping it there until you pass all three criteria for completion. Then to prevent additional problems you will need to keep your FC above 8 at all times to avoid further problems. So... how ok is 90 sounding? You'd be best to do a 50% water change before starting this process and bringing your CYA down.

TA is one of the last things to worry about. Actively reducing the TA level is rarely even worthwhile since just adjusting your pH will naturally bring the TA to a more stable level.

 

[thetekgeek]

I have to make a few assumptions because you did not specify what strength of bleach you are using. A gallon of 6% bleach should raise your FC to about 6 from .5 so I have assumed you are using 6%.

If so, you are running chlorine much too low for a CYA of 90. You probably have an algae bloom that is just on the verge of showing up. You need to be following the FC/CYA chart. Chlorine / CYA Chart - Trouble Free Pool Your target for a CYA of 90 is 10-12 and the minimum is 8. Since you have been below the minimum for quite some time, there is likely something growing in the water and you'll likely need to SLAM. Before you start that process though, I would suggest an OCLT. Add enough bleach tonight to get into the target range for your CYA and test after the sun is off the water. Test again tomorrow morning before the sun hits the water and compare the two values. If you have greater than 1 ppm of loss and/or CC is greater than .5 you will need to SLAM.

IF you do need to SLAM, you'd want to start by replacing a significant amount of water or you'll end up using an awful lot of bleach.

 

[jimbethesda]

Your target for a CYA of 90 is 10-12 so it NEVER falls below 7. Your target is below the minimum.

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com

You now likely have the start of an algae outbreak (not to mention your chlorine is likely too low to kill viruses and bacteria). You need to follow the SLAM process. Since your pool is not yet green, it should be quick.

SLAM - Shock Level and Maintain

We’ve all had to deal with a green pool. Clear algae from your pool with a SLAM! Read here to use shock level and maintain to clear your pool.

www.troublefreepool.com

 

[thetekgeek]

@Donldson beat me to it!

 

[Donldson]

Before you start that process though, I would suggest an OCLT.

OP has a CC level greater than 1.0 and already has demonstrated an overnight FC loss well outside 1 ppm. I think we can go ahead and forego the OCLT.

 

[thetekgeek]

OP has a CC level greater than 1.0 and already has demonstrated an overnight FC loss well outside 1 ppm. I think we can go ahead and forego the OCLT.

Agreed. Thank you for the clarification.

 

[bmj0928]

All great points. Thanks.

I've been using 10% Sodium Hypochlorite. Pool Math has been saying to add 120 oz. a day.

 

[bmj0928]

You won't find any of "those" here. You won't be agreeing with them either in a moment.

You have an issue that requires performing the SLAM Process. This will oxidize whatever is causing the CC issue as well as the organics that are almost certain to be contributing to the chlorine demand (CC and organics are two different sides of the same FC loss coin). As you'll find in the article, you need to follow the FC/CYA Levels to properly SLAM your pool. That means for a CYA of 90 raising your FC up to 35 and keeping it there until you pass all three criteria for completion. Then to prevent additional problems you will need to keep your FC above 8 at all times to avoid further problems. So... how ok is 90 sounding? You'd be best to do a 50% water change before starting this process and bringing your CYA down.

TA is one of the last things to worry about. Actively reducing the TA level is rarely even worthwhile since just adjusting your pH will naturally bring the TA to a more stable level.

Ok.... Time for a follow up question! Would you recommend a 50% water change all at once, or do it, say, 25% and 25%?

Also, can I water my lawn with this pool water? The last time I drained my pool a neighbor called the water authority on me because they thought there was a water main break.

 

[Donldson]

The more you can do in the first drain, the more efficient it will be. However, two 25% drains will bring you down to something reasonable so if that works better for you then go for it.

You should be able to water the lawn with the drained water. As long as you aren't giving it a diet of exclusively pool water, it won't hurt.

 

[bmj0928]

The more you can do in the first drain, the more efficient it will be. However, two 25% drains will bring you down to something reasonable so if that works better for you then go for it.

You should be able to water the lawn with the drained water. As long as you aren't giving it a diet of exclusively pool water, it won't hurt.

Thanks for all of your help. It's difficult to calculate what a 50% drain is given the shape and strangeness of my pool, so I eye balled it. I think I am ultimately going to end up at about 50 CYA, but the pool is still has a couple hours left to fill, so we'll see. A reduction of 45% is decent, though, especially because we only have a few months left to enjoy. I usually need to drain about 25% to close. I should be able to get through the rest of the season with 50 CYA.

Also, I removed my chlorinator while the pool was draining. I never really liked it, anyway. It was basically a chemical assault every time I opened it to add pucks. I'm a liquid convert... not ready for salt, yet.

 

[Oly]

How are you testing your water?

 

[bmj0928]

How are you testing your water?

TF-100

 

[bmj0928]

OK, the water replacement is complete, and I did another complete test. Levels are looking much better all around. Now, instead of needing 120 oz of 10% NaClO, I only need 77 oz.
*Edited: After reading some posts, I am going to begin the SLAM tonight.

FC = 0.5
CC = 1.0
pH = 7.2
TA = 90
CH = 325
CYA = 50
Temp = 86° F
CSI = -0.31